1Semaphore(3)                     OCaml library                    Semaphore(3)
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NAME

6       Semaphore - Semaphores
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Module

9       Module   Semaphore
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Documentation

12       Module Semaphore
13        : sig end
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16       Semaphores
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18       A semaphore is a thread synchronization device that can be used to con‐
19       trol access to a shared resource.
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21       Two flavors of semaphores are provided: counting semaphores and  binary
22       semaphores.
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25       Since 4.12
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33   Counting semaphores
34       A  counting semaphore is a counter that can be accessed concurrently by
35       several threads.  The typical use is to synchronize producers and  con‐
36       sumers  of  a  resource  by counting how many units of the resource are
37       available.
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39       The two basic operations on semaphores are:
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41       -"release" (also called "V", "post", "up", and "signal"), which  incre‐
42       ments the value of the counter.  This corresponds to producing one more
43       unit of the shared resource and making it available to others.
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45       -"acquire" (also called "P", "wait", "down", and "pend"),  which  waits
46       until  the counter is greater than zero and decrements it.  This corre‐
47       sponds to consuming one unit of the shared resource.
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50       module Counting : sig end
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57   Binary semaphores
58       Binary semaphores are a variant of counting semaphores where semaphores
59       can only take two values, 0 and 1.
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61       A binary semaphore can be used to control access to a single shared re‐
62       source, with value 1 meaning "resource is available" and value 0  mean‐
63       ing "resource is unavailable".
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65       The  "release" operation of a binary semaphore sets its value to 1, and
66       "acquire" waits until the value is 1 and sets it to 0.
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68       A binary semaphore can be used instead of a mutex (see module  Mutex  )
69       when  the mutex discipline (of unlocking the mutex from the thread that
70       locked it) is too restrictive.  The "acquire" operation corresponds  to
71       locking  the  mutex,  and  the "release" operation to unlocking it, but
72       "release" can be performed in a thread different than the one that per‐
73       formed  the  "acquire".  Likewise, it is safe to release a binary sema‐
74       phore that is already available.
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76       module Binary : sig end
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84OCamldoc                          2022-02-04                      Semaphore(3)